1. Technical Field
The present invention relates to the field of medical devices, and more particularly, to a positioning device with sensing capacities.
2. Discussion of Related Art
FIG. 1A is a schematic illustration of the epidural space and surrounding anatomical structures with a needle properly inserted into the epidural space according to the prior art. FIG. 1A illustrates the final stage of an epidural access procedure. A tip 92 of a needle 94 is positioned inside epidural space 70, for administering a medication through syringe 90 into epidural space 70, after being inserted through skin 30 and advanced between spinous process 55 and through the subcutaneous fat layer 40, supraspinous ligament 50, interspinous ligament 52 and ligamentum flavum (LF) 60.
Overshooting of the tip of the needle beyond epidural space 70 may puncture dura mater 80 causing a leak of the cerebral-spinal fluid (CSF) from around spinal cord 85 into epidural space 70, leading to severe headaches (post dural puncture headaches syndrome).
The majority of current injection techniques are “blind” techniques, mainly tactile based. For example, the main technique of epidural access is based on the “loss of resistance technique” (LORT). In LORT, a fluid or air filled syringe is attached to a needle. While needle 94 is advanced through different layers in the insertion site, the physician taps on syringe 90. Inside dense ligament layers, the physician feels a strong resistance, but when crossing ligamentum flavum 60 and entering epidural space 70, there is a substantial loss of resistance so that the fluid or air from syringe 90 can be easily pushed into the low-pressured epidural space 70, thus signaling the physician to stop advancing needle 94.
FIGS. 1B-1E are schematically illustrated cross sectional views of the stages of a typical epidural access procedure, according to the prior art, including the penetration of ligamentum flavum 60 and including entering into epidural space 70. When needle 94 is advanced through ligamentum flavum 60, the elastic fibers of ligamentum flavum 60 are stretched by the pushing pressure exerted by needle 94 deep into epidural space 70, before entering epidural space 70 (see FIGS. 1C and 1D). When the fibers reach a certain displacement, ligamentum flavum 60 ruptures and needle 90 penetrates into epidural space 70, as depicted in FIG. 1E, typically stopping a short distance (d1) from dura mater 80 (and in some cases even touching dura mater 80). The displacement required for the fibers of ligamentum flavum 60 to rupture differs from one person to another due to physiologic variations in ligamentum flavum elasticity, thickness and other factors. However, using the prior art technique has an extensive risk of accidently puncturing dura mater 80 due to overshooting of needle 94.